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What is Real?

Adam Becker
Basic Books
Publication Date: 
Number of Pages: 
[Reviewed by
Michael Berg
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In Hamlet, Act 1, Scene 4, we encounter the following from Horatio:

What if it tempt you toward the flood, my lord,
Or to the dreadful summit of the cliff
That beetles o’er his base into the sea,
And there assume some other horrible form,
Which might deprive your sovereignty of reason
And draw you into madness? think of it:
The very place puts toys of desperation,
Without more motive, into every brain
That looks so many fathoms to the sea
And hears it roar beneath.

The “it” that tempts Hamlet is the ghost of his father, and Horatio is filled with foreboding and dread. Hamlet succumbs to the temptation:

My fate cries out,
And makes each petty artery in this body
As hardy as the Nemean lion’s nerve.
Still am I call’d. Unhand me, gentlemen.
By heaven, I’ll make a ghost of him that lets me!
I say, away! Go on; I’ll follow thee.

And so it is that his friends, Horatio and Marcellus, let him go and he follows his father’s ghost. Subsequently we get the following exchange between Hamlet’s two comrades:


Let’s follow; ‘tis not fit thus to obey him.


Have after. To what issue will this come?


Something is rotten in the state of Denmark.


Heaven will direct it.


Nay, let’s follow him.

And there it is, then, a critical opening episode in one of the greatest tragedies ever written. Competitors for the title are, well, other plays by Shakespeare, maybe Macbeth, or King Lear, or what about The Merchant of Venice? — it’s like dealing with Beethoven or Michelangelo.

But what does this have to do with quantum mechanics and, specifically, the book under review? The answer is multifaceted, with complementary themes interweaving, just like … quantum mechanics. And the book in question deals explicitly with what some consider, indeed, to be “something rotten” in quantum physics, namely the vaunted Copenhagen interpretation. Is there indeed something wrong in this state of Denmark?

The history of the question, or of the controversy, is famous, going back to none other than Albert Einstein himself, who, while a major player in the early days of quantum theory, increasingly opposed it as it took shape under the auspices, largely, of his Danish friend and sparring partner, Niels Bohr. Einstein’s famous comment, in opposition to the evolving Copenhagen interpretation of quantum mechanics, was that “God does not play dice with the universe,” this in opposition to the non-classical statistics that were becoming enshrined in the subject. In fact, the philosophy hiding in the shadows, but just barely, was positivist and empiricist and involved everything from sacrificing causality to non-locality and launching weird and weirder paradoxes. The ghost of Hamlet’s father indeed pulled the generation of Wunderkinder of quantum physics toward “the flood … or the dreadful summit of the cliff,” and all were headed toward Denmark, including Werner Heisenberg, Wolfgang Pauli, to a lesser extent Paul Dirac, and, obliquely, Erwin Schrödinger — on the other hand, the latter proved to be something of a problem: see below. But nothing succeeds like success, and quantum mechanics’ claim to legitimacy rested on its efficacy, on its results’ agreement with experiments, and on what St. Thomas Aquinas calls the least persuasive form of argument (“according to Boethius” — the saint was not averse to a joke, even in the Summa Theologiae), namely, appeal to authority: Niels Bohr put his considerable weight behind it.

Despite the popular victory enjoyed by Bohr, and his making acolytes of nearly the entire physics establishment, there remained in place a small but loyal opposition. Indeed, already from the beginning, the world’s greatest and most famous physicist never gave in: Einstein quipped that the zealous quantum mechanics had not yet discovered “the thoughts of the Old One,” der Alte. And there were others, most notably one of QM’s founders, Schrödinger, the man who had developed wave mechanics, as well as the particularly controversial David Bohm. Even Dirac was more cautious about things than Bohr and his tribe.

At the Fifth Solvay Congress in 1927 the battle was joined for all the world to see: Einstein would have none of it, and Bohr dug in. Eight years later Einstein, together with Boris Podolsky and Nathan Rosen, introduced what is now called the Einstein-Podolsky-Rosen (or just EPR) Paradox into the debate, purporting to demonstrate that QM were an incomplete description of reality, with so-called hidden variables in the game. This is the crux of the matter: is QM in statu quo adequate to the task of dealing with “the real” or are there things missing?

In a broader context Einstein voiced the opinion that there could be no such thing as a final physical theory, and this position certainly has a good deal philosophical resonance to it for mathematicians as well as philosophers. A propos, in his later years, at the Institute of Advanced Study, Einstein described his daily walks home with Kurt Gödel as one of the great privileges and joys of his life. Indeed, Gödel is a very interesting actor in this play given his radical position on the very question of physical reality, or, rather reality generally. Gödel held that mathematical objects’ reality should be at least on a par with that of (to rip Hilbert off) tables, chairs, and beer-mugs, so he should probably locate himself orthogonally to Copenhagen. More to the point as far as our discussion is concerned, Gödel is of course famous for proving, among other things, the incompleteness of mathematics itself: could theoretical physics be any different? Given the relation of physics to mathematics, is reality only a special case, as the joke goes? Doesn’t this greatest logician since Aristotle have the last word, then?

And we have at last closed in on the book under review, with its pithy title and subtitle. Yes, the author, Adam Becker, proposes that the meaning of quantum physics is still very fluid and not at all fixed, the Copenhagen interpretation notwithstanding. He tells a spell-binding story with all the players strutting and fretting their hours upon the stage, and they are of course heard still. He splits his book into three parts, the titles describing the orbit of all things quantum. Part I deals with “A tranquilizing philosophy,” which indeed “might deprive [one’s] sovereignty of reason and draw [one] into madness …” — Richard Feynman himself once noted that “if you think you understand quantum mechanics, you don’t understand quantum mechanics.” Yikes. Well, Becker goes on to present Part II, viz., “Quantum dissidents,” and we meet Einstein, David Bohm, and John Bell, who is introduced to the reader with the chapter, “The most profound discovery of science.” And here we come to the aforementioned crux of the matter, i.e. the thesis that QM should be incomplete in virtue of a hidden variables hypothesis. It was John von Neumann who had early on argued against hidden variables, and consensus had it that he had pronounced the final word on the matter: Copenhagen vincit. But here is what Becker has to say on p. 145: “Bell took the opportunity away from his usual work at CERN to … figure out where von Neumann had gone wrong … He found that von Neumann’s revered proof, consistently invoked against any heresy, was hardly a proof at all … The great John von Neumann had simply made a mistake — he [had] made assumptions in his proof that were entirely unwarranted …”

Bell’s resulting opposition to the Copenhagen interpretation’s prohibition on hidden variables additionally involved support for the work of the controversial David Bohm, centered on the notion of pilot waves. Indeed, there are parallels between Bohm’s ideas and de Broglie’s, dating back to the 1927 Solvay Congress. The point is that e.g. “[t]he effect of … measurements on … photons’ pilot waves alters their trajectories, causing them to form a pair of clusters on the photographic plate [used in the fundamental double-slit experiment] rather than an interference pattern,” and this suffices to take the wind out of the sails of the Copenhagen interpretation. Becker goes on to say, “[i]n Bohm’s account, although measurement can influence a particle’s motion, all particles have definite positions whether or not anyone is looking at them.” Wow! This is a full-frontal assault on the centerpiece of the Copenhagen interpretation of QM, the uncertainty principle of Heisenberg.

All right, then, what’s the story? Do we go with Bohm? Well, not quite (yet): on p. 111 Becker gets down to brass tacks: “… because Bohm’s theory involved faster-than light connections between particles, it appeared difficult to extend Bohm’s ideas to incorporate special relativity,” and so, yes, this is truly a sticky wicket. Becker’s account of all this is really a page-turner. We learn about Bohm’s interaction with Schrödinger and Einstein, all while Bohm was exiled to Brazil due to his being in the crosshairs of the House Un-American Activities Committee. Here are two appraisals by Becker: “… just as in Solvay twenty-five years earlier, the defenders of the Copenhagen interpretation presented a unified front despite their private disagreements [!], while the rebellion, unable to agree on a single position, fizzled out …” (p. 114), and “… the pilot-wave interpretation sank into obscurity as Bohm searched for a new way to understand the quantum world.

But back at Princeton, where all his troubles began, a new alternative had already been found …” (p. 116). And this new way was due to Hugh Everett: the so-called many-worlds interpretation of quantum mechanics. Here’s Becker again (pp. 138–139):

Everett’s theory slipped into a deep obscurity for the next decade, provoking almost no immediate reaction — certainly not the kind of fierce backlash that Bohm’s papers had prompted. The universal wave function was simply ignored … [Everett] never took the debate to a larger arena … The wider stage of academia held no allure for him … [and] he felt no particular need to remedy the physics community’s misguided manner of thinking about quantum physics. That task would take a different sort of person … It took someone who had always known Copenhagen was rotten, who had seen David Bohm do the impossible. It took … John Stewart Bell.

And so we finally come to Bell’s theorem. What does it say? Well, see pp. 141-162. But here’s the thrust: it involves a souped-up version of ERP and leads to three mutually exclusive possibilities: “either nature is non-local in some way, or we live in branching multiple worlds despite appearances to the contrary, or quantum physics hives incorrect predictions about certain experimental setups” (p. 160). And then: “No matter the outcome, Bell’s work presents a threat to the Copenhagen interpretation …” Again, Wow! To get back to Hamlet: “There are more things in heaven and earth, Horatio than are dreamt of in your philosophy” (Act 1, Scene 5).

On that note, with that famous quote from the Bard of Avon, let me close this (very positive but already too long) review, noting that there’s a lot more to be found in this nice book, and it’s all spellbinding: Becker writes very well, and he has good material to work with. To any one with more than a passing interest in QM, how it came to be the way it is, and how it might be otherwise, this book will be irresistible.

Michael Berg is Professor of Mathematics at Loyola Marymount University in Los Angeles.

The table of contents is not available.